An electric stapler in which stacked staple sheets each composed of linear staples connected in parallel are loaded is used as not only a stand-alone stapler but also incorporated in a copier or post-printing processor.
As a kind of electric stapler, there has been proposed an electric stapler using a staple magazine in which stacked staple sheets are loaded. In this electric stapler, when the staples are used up, an entire magazine is replaced. JP-A-2004-237446 discloses an electric stapler in which for the purpose of resource-saving, a staple for refill is received within a case of plastic paper, and the case is loaded in a staple magazine or an electric stapler body.
The staple for refill proposed in JP-A-2004-237446 is provided with a plate-shaped pushing member for pushing staple sheets within a plastic case from above. When an arm or spring provided in the staple magazine or the electric stapler body depresses the pushing member, the pushing member is brought into elastic contact with an upper face of the staple sheets. Thus, a staple sheet on a lowermost layer is stably fed to a forming-and-driver mechanism.
The staple for refill proposed in JP-A-2004-237446 is accommodated in a plastic case and has a structure in which a plate-shaped pushing member is placed on an upper face of the staple sheets. A depressing means such as a spring for urging the pushing member is provided on a side of the staple magazine or the electric stapler body. Therefore, in a state where the depressing means is not loaded in the staple magazine or electric stapler, pushing of the staple sheets is released so that the staple sheets may move up and down, or fly out from the staple forwarding mouth of the case.
In order to obviate such an inconvenience, in accordance with a related art of this application which is not a prior art, sawtooth nonreturn projections are arranged vertically in parallel on an inner wall of the case and a nonreturn lug engaged with the nonreturn projections are provided on a plate-shaped pushing member so that a rise of the plate-shaped pushing member is limited. In accordance with this related art, a component such as a spring is not required so that the structure is simple. In addition, since the metallic component is not used, disposal processing can be easily carried out.
However, in this case, since depressing of the plate-shaped pushing member while the electric stapler is used is entrusted to a spring on a side of a staple magazine or a stapler body, as the staple sheets are consumed and the plate-shaped pushing member descends, a load of the spring decreases so that an elastic force of the spring is problematically reduced.
Specifically, as a result that the spring on the electric stapler depresses the plate-shaped pushing member, when the nonreturn lug of the plate-shaped pushing member warps and climbs over the nonreturn projections, a certain load is applied. If the plate-shaped pushing member is located at a relatively raised position (when there are many remainders of the staple sheets), the spring is compressed to provide a large elastic force so that depressing of the plate-shaped pushing member is not problematic. However, as the plate-shaped pushing member descends owing to consumption of the staple sheets, the spring is expanded and so its elastic force is also reduced. In this case, the nonreturn lug of the plate-shaped pushing member cannot climb over the nonreturn projections so that the plate-shaped pushing member may not be in pressure-contact with the staple sheets.